Field of the Invention
The present invention relates to recovery processing of the sharpness of an image formed by an image forming apparatus.
Description of the Related Art
It is known that the sharpness of an image output from an image forming apparatus degrades due to misalignment of the landing position of ink, the spread of ink, an optical blur (optical dot gain), or the like. If the frequency characteristic (to be referred to as a “sharpness degradation characteristic” hereinafter) of sharpness degradation of the output image can be obtained, sharpness degradation can be canceled by recovery filter processing having the opposite characteristic.
Note that the sharpness degradation characteristic is different depending on the type of image forming apparatus (inkjet method, electrophotographic method, or the like), a model, the type of print medium (print sheet), an output condition, a light source distribution (angle and direction) at the time of viewing of an image, and the like. In, for example, an image forming apparatus using the inkjet method, the sharpness degradation characteristic changes in accordance with differences in the spread of ink depending on an ink type (dye or pigment), an optical dot gain at the time of viewing, a print medium, and the like.
Japanese Patent Laid-Open No. 2013-61925 (literature 1) describes a technique of performing sharpness recovery processing using a different sharpness recovery filter in accordance with a print medium, ink type, an input device, and a portion of an object. In this technique, the sharpness degradation characteristic of an output image and a sharpness recovery filter have a one-to-one correspondence. As a result, since it is necessary to hold sharpness recovery filters for all combinations of the items of an output condition, such as a print medium, ink type, pass count, carriage speed, scanning direction (two-way or one-way printing), and halftone processing, the technique is not practical.
The technique in literature 1 cannot cope with unknown print media (unregistered print media) at all. Furthermore, although the appearance (degradation characteristic) of the sharpness of an output image is different depending on an illumination position at the time of viewing of the image, the technique in literature 1 does not consider this point.